Single-Shaft Vacuum Positive Displacement Pump

ABSTRACT

A single-shaft vacuum positive displacement pump ( 10 ) comprises two pump stages ( 12,14 ) each provided with a pump rotor ( 13,15 ) and a drive motor ( 16 ). The drive motor ( 16 ) is axially arranged between the two pump stages ( 12,14 ), wherein the shaft ( 22 ) supports the pump rotors ( 13,15 ) and the motor rotor ( 17 ).

The invention relates to a single-shaft vacuum positive replacement pumpcomprising two or more pump stages arranged one behind the other and adrive motor.

Conventional single-shaft vacuum positive replacement pumps comprisingtwo pump stages are configured as two-stage rotary piston pumps orrotary vane pumps, for example. Usually, the two pump stages are axiallyarranged one behind the other, wherein the drive motor is disposed at alongitudinal end of one of the two pump stages and drives the commonshaft of the two pump stages. Both the drive motor and the two pumpstages are arranged in their own housings such that the shaft passesthrough a plurality of housing openings. For shaft supporting purposesat least two shaft bearings are provided in the drive motor, and in theregion of the pump stages three shaft bearings are normally arranged.

It is an object of the invention to provide a simplified single-shaftvacuum positive replacement pump.

According to the invention, this object is achieved through the featuresof claim 1.

In the positive replacement pump according to the invention, the drivemotor is axially arranged between the two pump stages, wherein a singlecommon shaft supports the two pump rotors and the motor rotor. Thevacuum positive replacement pump thus only comprises a single one-pieceshaft, which offers a number of constructional advantages. In particulartwo common shaft bearings can be used for supporting the drive motorrotor and the two axially adjacent pump rotors. In this manner, thenumber of shaft bearings can be reduced to only a few bearings. When thetwo pump rotors are supported in a cantilevered position, the overallpositive replacement pump does not require more than two shaft bearings.Due to the single-shaft configuration a coupling is not required, whichfurther simplifies the layout. Thus a simple two-stage positivereplacement pump of compact design, which is inexpensive to manufacture,is provided. To the two pump stages arranged adjacent to the drive motorfurther pump stages facing away from the drive motor may be axiallyattached.

Preferably, the gas connection between the two pump stages is defined bythe gap between the motor rotor and the motor stator. Formation of a gapbetween the motor rotor and the motor is unavoidable. This gap serves asa connecting conduit between the two pump stages, namely between theprevacuum stage and the high-vacuum stage. A separate connecting conduitbetween the two pump stages thus need not be provided. This allows for asimple configuration and an inexpensive manufacture. An additionalseparate connecting conduit is to be provided merely in the case of alarger pumping capacity.

According to a preferred embodiment, the gap between the motor rotor andthe motor stator is cylindrical, i.e. the motor rotor is of cylindricalconfiguration on the outside, and the motor stator is of cylindricalconfiguration on the inside.

According to a preferred embodiment, the motor rotor comprises a helicalpump groove. The helical rotating pump groove improves the axial gastransport from the high-vacuum stage to the pre-vacuum stage through thegap between the motor rotor and the motor stator.

According to a preferred embodiment, the motor rotor acts as a lubricantpump pumping the lubricant from the upstream to the downstream pumpstage. In wet-type vacuum positive replacement pumps, i.e. in positivereplacement pumps lubricated with a flowing lubricant, the pump grooveis suitable for transporting even the liquid lubricant from thehigh-vacuum stage to the pre-vacuum stage. Therefore a separatelubricant pump is not required. The lubricant further cools the drivemotor and in particular the motor rotor such that a separate motorcooling device may possibly be omitted.

Preferably, a single stator housing surrounds the shaft, wherein thestator housing does not comprise any shaft sealings. The stator housingthus surrounds the two pump stages and the motor rotor, and may possiblydefine the stators of the pump stages and the drive motor. Since noshaft sealings are provided, all problems and costs associated therewithare avoided. In particular any undesired oil and gas leakage can thus beprevented to a large extent.

Preferably, the stator housing is surrounded by a lubricant housing. Thestator housing is arranged in spaced relationship in the lubricanthousing such that the lubricant is disposed between the stator housingand the lubricant housing, and is allowed to flow from the outlet to alubricant pump.

Preferably, the two pump stages are configured as rotary piston orrotary vane pump stages. Multistage rotor stages or claw-type pumpstages or other types of pump stages may also be provided.

An embodiment of the invention will now be described in greater detailwith reference to the drawings.

The FIGURE shows a longitudinal section of a single-shaft vacuumpositive replacement pump according to the invention comprising tworotary vane pump stages.

The FIGURE shows a vacuum positive replacement pump 10 comprising twopump stages 12,14 each configured as a rotary vane pump stage, and adrive motor 16 axially arranged between the two pump stages 12,14. Theinlet-side pump stage 14 is connected with a gas inlet 18 and definesthe high-vacuum stage. The pump stage 12 arranged downstream as seen inthe direction of gas flow is the pre-vacuum stage which pumps gasagainst the atmospheric pressure out of the gas outlet 20. The two pumpstages 12,14 each comprise a pump rotor 13,15, and the drive motor 16comprises a motor rotor 17. The pump rotors 13,15 and the motor rotor 17are permanently fixed to a common one-piece shaft 22. The motor rotor 17is permanently excited.

The gas connection between the two pump stages 12,14 is realized by acylindrical gap 24 which is defined on the inside by the motor rotor 17and on the outside by a motor stator 28. The motor rotor 17 comprises ahelical groove 30 provided in the cylindrical outside of the motor rotor17. The gas connection may further be realized by an external channel,e.g. in the case of larger pumping capacities.

The shaft 22 is supported by two shaft bearings 32,34 configured asroller bearings. Slide bearings or gas bearings may also be used. Thepump rotors 13,15 are supported in a cantilevered position such that theshaft 22 is supported by the two shaft bearings 32,34 alone.

The two pump stages 12,14 and the drive motor 16 as well as the shaft 22are supported and fully surrounded by a stator housing 40. The statorhousing 40 does not comprise any shaft sealings. The stator housing 40,in turn, is arranged in a lubricant housing 41 which serves forreceiving the lubricant and transporting it from the pre-vacuum side tothe high-vacuum side.

At the high-vacuum end of the shaft 22 a gear pump 44 is arranged whichpumps the liquid lubricant 46 into the gap 24 between the motor rotorand the motor stator via a channel 48. Through a corresponding inlet asmall portion of the lubricant delivered by the gear pump 44 istransported directly into the working chamber of the high-vacuum pumpstage 14. The mixture of the gas and the lubricant leaving thehigh-vacuum pump stage 14 is pumped to the pre-vacuum pump stage 12 viathe helical pump groove 30, whereby the motor rotor 17 and the motorstator 28 are lubricated and cooled.

Adjacent to the pump chamber outlet of the pre-vacuum pump stage 12 anoil separator 50 is arranged which separates the lubricant dripping downand the the gas pumped off against the atmosphere. The lubricant flowsbetween the lubricant housing 41 and the stator housing 40 and back tothe gear pump 44.

1. A single-shaft vacuum positive displacement pump comprising: two pumpstages, each stare including a pump rotor; and a drive motor said drivemotor being axially arranged between said two pump stages, and a shaftsupporting pump rotors of said pump stages and a motor rotor.
 2. Thesingle-shaft positive displacement pump according to claim 1, wherein agas connection between the two pumps stages is defined by a gap betweenthe motor rotor and a motor stator.
 3. The single-shaft positivedisplacement pump according to claim 2, wherein the gap between themotor rotor and the motor stator is cylindrical.
 4. The single-shaftpositive displacement pump according to claim 2, wherein the motor rotorcomprises a helical pump groove.
 5. The single-shaft positivedisplacement pump according to claim 1, wherein a stator housingsurrounds the shaft, wherein the stator housing does not comprise anysealings.
 6. The single-shaft positive displacement pump according toclaim 1, wherein exactly two roller bearings are provided between themotor rotor and the pump rotors.
 7. The single-shaft positivedisplacement pump according to claim 1, wherein a stator housing issurrounded by a lubricant housing.
 8. The single-shaft positivedisplacement pump according to claim 1, wherein the motor rotor acts asa lubricant pump which pumps a lubricant from a high-vacuum one of thepump stages to a downstream pre-vacuum one of the pump stages.
 9. Thesingle-shaft positive displacement pump according to claim 1, whereinthe two pump stages are configured as rotary piston or rotary vane pumpstages.
 10. The single-shaft positive displacement pump according toclaim 1, wherein a first bearing and a first of the pump stage rotorsare supported on the shaft on one side of the motor rotor and a secondbearing and a second of the pump stage rotors are supported on the shafton an opposite side of the motor rotor.
 11. A pump comprising: a motorstator; a motor rotor rotatably mounted in the motor stator on a shaft,the motor rotor and the motor stator defining a fluid passagetherebetween; a first pump stage having a rotor mounted on the shaft onone side of the rotor to pump fluid from a fluid inlet into the fluidpassage between the motor rotor and the motor stator; and a second pumpstage having a rotor mounted on the shaft on an opposite side of therotor from the first pump stage rotor to pump fluid from the fluidpassage between the motor rotor and the motor stator to an outlet. 12.The pump according to claim 11 further including: a first bearingsupporting the shaft between the motor rotor and the first pump stagerotor; and a second bearing supporting the shaft between the motor rotorand the second pump stage rotor.